1. Field of the Invention
The present invention relates to a hybrid induction motor, and more particularly, to a hybrid induction motor capable of improving a starting function and facilitating to implement a variable speed rotation.
2. Description of the Background Art
A hybrid induction motor refers to a motor in which a permanent magnet (hereinafter, will be referred to as a ‘synchronous rotor’) is free-rotatably installed between a stator and an induction rotor thus to be electro-magnetically coupled thereto.
FIG. 1 is a longitudinal section view showing a hybrid induction motor in accordance with the conventional art, and FIG. 2 is a sectional view taken along line I-I of FIG. 1.
As shown, in a conventional hybrid induction motor 10, a stator 11 is fixedly-disposed at an inner side of a casing 10a, and a synchronous rotor 14 is rotatably disposed at an inner side of the stator 11. An induction rotor 13 is rotatably disposed at an inner side of the synchronous rotor 14. Also, a rotation shaft 15 for outputting a rotation force of the induction rotor 13 outwardly is press-fit into a center of the induction rotor 13.
The stator 11 is formed of a laminated silicon steel, and a plurality of slots 16a for winding a driving coil 16 that generates a rotating magnetic field are formed at an inner circumferential surface of the stator 11.
The synchronous rotor 14 comprises a magnet portion 14a freely rotatable between the stator 11 and the induction rotor 13, a magnet support portion 14b for supporting the magnet portion 14a, and a bearing portion 14c for supporting the magnet support portion 14b to freely rotate around the rotation shaft 15.
The induction rotor 13 is formed as a squirrel cage rotor comprising a plurality of through holes 13a formed in the laminated silicon steel with, conductive bars 13b inserted into each through hole 13a, and end rings 13c formed at both ends of each conductive bar 13b. An unexplained reference numeral 15a denotes a shaft bearing.
An operation of the conventional hybrid induction motor will be explained.
Once a rotating magnetic field is formed as a first current is sequentially applied to the driving coil 16 of the stator 11, the synchronous rotor 14 is synchronized by the rotating magnetic field thereby to be rotated at a synchronous speed. A magnetic flux generated from the magnet portion 14a of the synchronous rotor 14 serves as a rotating magnetic field of the induction rotor 13, so that the induction rotor 13 is rotated.
Herein, the rotation shaft 15 coupled to the induction rotor 13 is rotated together with the induction rotor 13 thereby to transmit a rotation force to other components such as a fan.
However, in the conventional hybrid induction motor 10, a single synchronous rotor is implemented under a state that a magnetic flux density of an air gap between the induction rotor and the synchronous rotor is almost constant. Therefore, a starting torque of the synchronous rotor 14 is not sufficient, and thus a great current has to be applied to the driving coil 16 at the time of an initial driving of the induction motor.
Furthermore, even if a voltage applied to the driving coil 16 is varied, a varied amount of the magnetic flux density of the air gap is reduced, resulting in a difficulty in speed-varying the induction motor. Accordingly, an efficiency of the motor is degraded and the motor has limited functions.